This invention relates to a solution and method for preservation of cells at ambient temperatures. The solution and method provide rapid fixation of live cells for subsequent analysis.
It is known in the clinical and research arenas that preservation of cell samples for subsequent analysis is desirable. From a diagnostic standpoint, a specimen is most valuable when it is fresh. The more time that elapses between collection of a specimen and its fixation on a slide or other matrix, the less integrity is retained. Depriving cells of the physiologic conditions of its donor for long periods of time, i.e., minutes, allows autolysis to begin.
In a clinical setting it is often necessary to take samples, e.g., vaginal cells or muscle cells from a patient, which are later stained for histology analysis. Such histochemical staining has unquestionable value in the interpretation and study of cell physiology and pathology, however the staining cannot usually be performed simultaneous with the sampling. It is often-desirable to perform a biopsy on a patient at one time, and to perform cytological or histological analysis of the collected cells or tissue at a different time. Calls often lose integrity in that interim period, thus diminishing the value of the subsequent analysis.
Several types of saline, or balanced salt, solutions are commercially available for preserving cell specimens in the interim between sampling and fixation and/or analysis. A few of these solutions includes Hanks' balanced salt solution, a minimal essential (MEM) tissue culture medium, Polysal.RTM., and normal saline. The high cost of some medium, such as Hanks' and MEM, prohibits its routine use.
Polysal.RTM., available from Cutter Biologicals, Emeryville, Calif., is a balanced polyionic electrolyte solution containing sodium chloride, calcium, and magnesium at a physiologically equivalent concentration to normal human plasma. Although an adequate saline solution for relatively short-term storage, it neither inhibits bacterial growth nor enables extended ambient storage.
Hanks' BSS is a modified Ringer solution. It is designed to maintain osmotic pressure within physiologic limits, maintain optimal pH range by including buffer systems, and provides an adequate concentration of inorganic ions for normal cell metabolism. This solution includes a glucose energy source. However, cells lose viability after an exposure of over twenty minutes, which affects cytopathologic analysis.
Many types of clinical tissue and cell samples contain extraneous proteins which interfere with subsequent staining and analysis. Placement of specimen cells in a saline solution does not address some auxiliary problems with such sample integrity. Extended preservation of specimens often results in bacteria growth, which is also nurtured by the balance of prior art normal or augmented saline solutions.
Accordingly, it is an object of the present invention to provide a cell fixing solution and process which preserves cells and tissue for subsequent cytological or histological analysis.